1. Field of the Invention
The present invention relates to a vibration isolator for use in, for example, an ambulance for carrying sick or wounded people to make them more comfortable.
2. Description of the Related Art
Hydraulic or air suspensions are employed in most of the vibration isolators, and various measures have been taken up to this time to improve the riding comfort. Vibration isolators that perform an active control to improve the riding comfort have been proposed.
The running of ambulances includes ordinary running, in which they run with the stream of cars, and special running when they are called in an emergency. The riding comfort differs between the ordinary running and the special running.
In order to confirm the effects of the vibration isolators on the riding comfort, actual running tests were carried out using a typical domestic car and a typical imported car. During the tests, longitudinal (back and forth), widthwise (right and left) and vertical accelerations of a floor of an ambulance and those of the waist of a subject lying on a stretcher were measured and analyzed. The tests revealed that the conventional vibration isolators could achieve effective isolation in a high-frequency region (10-20 Hz), but could not satisfactorily restrain low-frequency vibrations (0.1-10 Hz), particularly the longitudinal and vertical low-frequency vibrations. For this reason, there arose the problems that the condition of a sick or wounded person may become worse due to resonance of his or her internal organs in particular, a fluctuation in blood pressure (a sense in which blood concentrates on the head) may be caused by a nose dive, or he or she may get carsick. Such problems were, however, sometimes caused by an improper adjustment of a suspension system of the vibration isolator to the vehicle body.